1. Field of the Invention
This invention relates to a continuous method for producing high impact resistant thermoplastic resins.
2. Description of the Prior Art
Acrylonitrile-butadiene-styrene copolymers (so called ABS resin), rubber modified polystyrenes (so called high impact polystyrene), and methylmethacrylate-butadiene-styrene copolymers (so called MBS resins) are valuable materials in the plastics industry. These rubber modified impact resistant thermoplastics resins are conventionally produced by emulsion polymerization. The polymers obtained according to conventional methods have excellent properties. However, in the processes of removing the polymers from the latices after polymerization, (i.e., by coagulation, dehydration, and drying) considerable deterioration of properties of the resins is encountered. Furthermore, the conventional processes are not satisfactory from an economic viewpoint.
In order to overcome the aforementioned problem methods have been devised wherein a vinyl monomer capable of being graft polymerized is added to the rubber polymer and the mixture is then subjected to bulk polymerization. However, heretofore satisfactory continuous bulk polymerization has not yet been obtained because removal of the great quantity of het generated during the polymerization is very difficult. Accordingly, control of polymerization temperature is difficult when the prior art processes are practiced on a commercial scale.
To control the polymerization temperature, it has been suggested to remove the heat of polymerization from the reaction system by taking off the monomer vapor alone or with a small quantity of water, condensing the monomer vapor and recycling the condensed monomer to the reaction mixture. This method must, however, be conducted under close control and at a rather relatively low conversion in the first polymerization stage, otherwise the reaction process is adversely affected resulting in the final polymer having and undesirable color and poor physical properties.
It has also been suggested to polymerize the monomer by using an initiator. But this method is not satisfactory because initiator remains in the final polymer which causes the deterioration of the polymer.
A further problem encountered by the methods heretofore suggested, is that the polymers obtained by conventional bulk polymerization are inferior to those obtained by emulsion polymerization in properties such as the impact resistance and luster. This is because it is difficult to obtain a homogeneous mixture of the reaction mixture in bulk polymerization because the viscosity of the reaction mixture is quite high.
It is accordingly an object of this invention to overcome the problems encountered with the prior art method of producing high impact resistant thermoplastic resins. The use of only a rubber polymer suspended in monomer solution, obtained by extraction of rubber polymer particles in latex with vinyl monomers, can accomplish this object.
It is a still further object of this invention to provide a continuous process for bulk polymerizing thermoplastic monomers so as to produce a high impact resin thermoplastic resin.
Another object of this invention is to provide a bulk polymerization method for producing high impact resistant resins continuously in which the heat of polymerization is effectively removed.
A still further object of this invention is to provide the continuous bulk polymerization method by which uniform mixing of the reaction system can be obtained.
Other objects and advantages of this invention will become further apparent hereinafter from a study of the drawing and a continued reading of the specification and subjoined claims.